When the size of electrical equipment is reduced, a space in which air flows inside a casing of the electrical equipment is also reduced. For this reason, as a fan used for cooling an inside of the casing, the fan characterized by an increased air volume and a higher static pressure is demanded. In the fan having such characteristics, it is also demanded to reduce noise as much as possible.
U.S. Pat. No. 6,244,818 or Japanese Patent Publication No. 2000-257597 (Patent Document 1), for example, discloses an axial flow fan including an impeller having nine rotary blades and 13 stationary blades disposed on the side of a discharge opening to fulfill this demand, as shown in FIGS. 1 and 4 of Patent Document 1.